Composite rubber piston



Feb. 4, 1936 GEYER 2,029,367

COMPOSITE RUBBER'PISTON Filed Aug. 3, 1934 INVENTOR HEIV'E)/ .U Beyer TTORNEYS I Patented Feb. 4, 719 36 UNITED STATES 1 PATENT OFFICE COMPOSITE RUBBER PISTON Harvey D. Geyer, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Micln, a cornotation of Delaware Application August a, 1934, Serial No. 738,178

5 Claims.

. I which is highly emcient and has a long life in use and yet is very simple. and economical to manufacture,

A more specific object is to provide an integrally molded composite piston of hard and flexible rubber, the hard rubber portion forming the bearing which slides upon the cylinder walls I while the flexible rubber portion forms the piston head which permits fluid to flow past same in one direction of movement but seals the fluidflow in the other direction of movement.

- Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing, wherein a preferred embodiment of the present invention is clearly shown.

In the drawing:

Fig. '1 is a longitudinal section through the piston made according to this invention and is taken on line of Fig. 2.

Fig. 2 shows the piston of Fig. 1 in side elevation in the master cylinder of a hydraulic braking system for automobiles.

Fig. 3 is a pivot end elevation of the piston looking in the direction of arrow 3 of Fig. 1.

Similar reference characters refer to similar parts throughout the several views.

The piston-3|) of this invention reciprocates within the master cylinder 3|. To apply the brakes in the device illustrated in Fig. 2, piston 30 is forced to the left (as viewed in Fig. 2) by any suitable mechanical linkage such as the rocking lever .32 and the connecting rod l5.

from cylinder 3| throlmh the duct 33 and-thence to the brake-actuating fluid motors and thus the brakes are applied. When it is desired to release I the brakes, piston 30 is returned to its position shown in Fig. 2 and the working fluid which was forced out of cylinder 3|through duct 33 returns Y times.

thereto through the same duct 33 due to the re.-

duction of pressure. The chamber 35 overlying" 7 during its compression or working stroke enters this reservoir 35, and when piston 30 is on its return stroke this escaped fluid returns to cyl- The working fluid, such as oil, is forced by piston 30 inder 3| past the flexible cup |2 of the piston as described hereinafter. Reservoir 35 communicates with the cylinder 3| through the passage 36 when piston 30 is in its fully withdrawn position in order to-insure that cylinder 3| is main- 6 tained completely filled with the working fluid at all times.

. The piston shown in'Fig. 1 comprises a hard rubber body l0 integrally molded with a flexible rubber piston'head having an integral ex- 10 pansible circular flange |2 thereon. The rubber piston body ID has a circular metal insert I3 molded in sltutherein and strongly bonded to the rubber by vulcanization in situ. Metal insert I3 has a slot l4 therein for receiving one 16 -end of the connecting rod l5 (see Fig. Zland a transverse hole l6 for receiving the pivot pin II- by means of which connecting rod I5 is suitably pivoted to the rear end of the piston of Fig. 1'. Thus the metal insert l3" provides a non-break- 20 able and rion-distortable reinforcement for the rubber portions of the piston and at the same time provides a suitable metallic bearing for the pivot connectionto the connecting rod I5. 111'- sert I3 is preferably of cold rolled steel and ma- 2 chined to the desired dimensions before being located as an insert in the cavity of the vulcanizing mold. The uncured rubber blanks to form the rubber portions l0 and H are separately c'ompoundedso as to producethe desired hard and so soft rubber respectively when cured simultaneously in the vulcanizing mold, and these two rubber portions will. of course be integrally-bonded together during the vulcanization. There will be no sharp line of division between the hard and 35 soft rubber portions l0 and H since the greater percentage of sulphur and accelerator in the blank for portion ID will have some vulcanizing effect on the adjacent portions of the blank for. portion during vulcanization. Preferably therubber at the lips of the cup II is the softest and its hardness increases gradually to a point adjacent the closest end of the metal insert l3. The line 20 in Fig. 1 indicates the line of division between the two uncured blanks prior to vulcanization. Y

A series of grooves 25 are molded in the surface of the hard rubber body In .to provide for easier return of the fluid from the back end to the front end of the piston during the rearward movement. thereof. These grooves 25 taper off to zero before they reach the lip of the flexible cup flange l2, as clearly shown in Fig. 1. Thus it will be seen that when the piston moves rearwardly the fluid in grooves 25 may pass easily to the front end of the piston by the inward flexure of the flexible flange l2, but upon forward movement of the piston this flexible flange I2 is expanded by the compressed fluid into sealing engagement with the cylinder walls and thus completely closes all the ducts 25. The expansible cup flange I! thus serves as a simple one-way valve for all the ducts 25.

The hard rubber body Ill may have any desired amount of graphite compounded therein to provide a suitable anti-friction bearing surface which slides against the cylinder walls. In any 7 case the friction and wear of the hard rubber body l0 against the cylinder walls will be smaller than a similar surfaces.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

' What is claimed is as follows:

1. A one-piece unitary piston for a hydraulic brake cylinder; comprising: an integrally molded flexible rubber piston head and hard rubber body, said hard rubber body having a metal insert vulcanized in situ therein and having a pivot attachment means for connection to a connecting rod.

2. A unitary piston for a hydraulic brake cylinder, comprising: a metal insert having a pivot attachment to a connecting rod, a hard rubber casing surrounding said metal insert and bonded thereto by vulcanization in; situ and forming the bearing surface for contacting the cylinder walls,

. to said hard rubber casing.

rubbing together of two metal and a flexible rubber cup head integrally molded 3. A unitary piston for a hydraulic brake cylinder, comprising: a metal insert having a pivot attachment to a connecting rod, a hard rubber casing surrounding said metal insert and bonded thereto by vulcanization in situ and forming the bearing surface for contacting the cylinder walls,

said rubber casing having a longitudinally ex-' tending groove formed in its surface and providing a duct from the pivot end to the head end of the piston, and a flexible rubber cup head integrally molded to said hard rubber casing.

4. A one-piece unitary piston for a hydraulic brake cylinder, comprising: an integrally molded flexible rubber piston head and hard rubber body, said hard rubber body having a metal insert vulcanized in situ therein and having a pivotattachment means for connection to a connecting rod, said hard rubber body having a duct groove formed in its surface and leading from the pivot end to the flexible rubber head, said flexible rubber head forming a closure for said duct when it is expanded by fluid pressure.

5. A one-piece unitary piston for a hydraulic brake cylinder, comprising: an integrally molded flexible rubber piston head and hard rubber body, said hard rubber body having a metal insert vulcanized in situ therein and having a pivot attachment means for connection to a connecting rod, said piston having a fluid-conveying duct leading from the pivot end to a point adjacent I the flexible rubber head, said flexible rubber head forming a closure for said duct when it is expanded by fluid pressure acting upon the head.

- HARVEY D. GEYER. 

